Progressing cavity helical pump



May 19, 1970 c. H. ALLEN 3,512,904

PROGRESSING CAVITY HELICAL PUMP Filed May 24, .1968 3 Sheets-Sheet 1ATTORNEYS May 19; 1970 c. H. LLEN 3,512,904

PROGRESSING CAVITY HELICAL PUMP Filed May 24, 1968 3 Sheets-Sheet 2ATTOP/Vf Y5 y 1970 c. H. ALLEN 3,512,904

PROGRESSING CAVITY HELICAL PUMP Filed May 24, 1968 3 Sheets-Sheet 5INVENTOR CZ/FFURO AZAEA/ Bum $5 MM.

WWWU L ATTO/QA/EYJ United States Patent 0,

3,512,904 PROGRESSING CAVITY HELICAL PUMP Clifford H. Allen, 13109Westchester Trail, Chesterland, Ohio 44026 Filed May 24, 1968, Ser. No.731,828 Int. Cl. F04c 1/06, 5/00, 17/14 U.S. Cl. 418-48 7 ClaimsABSTRACT OF THE DISCLOSURE A progressing cavity, positive displacement,helical pump or motor for handling fluid or comminuted materials. Thedevice forces material axially through helical cavities defined by astator with a helical interior surface and an eccentric rotor with ahelical exterior surface, the rotor being operatively connected througha spindle or hinged joint to a rotary drive.

BACKGROUND OF THE INVENTION This invention relates toprogressing-cavity-type positive displacement helical pumps and motorsand especially to planetary rotor type pumps for handling both fluidsand comminuted materials such as food products, chemicals, sludge,concrete mix and the like. More particularly the invention relates to animproved planetary rotor and stator design which affords improvedsealing of the cavities with reduced wear and which eliminates the needfor a universal connection between the rotor and the rotary drive.

Such pumps generally comprise a pair of helical threaded elements insealing engagement with one another cooperating to produce a series ofpumping pockets or cavities which travel axially through the pump fromone end to the other. Normally the outer member is a stator with anaxial cavity having a helical internal surface and the inner member is arotor positioned within the stator and having a helical external surfacewith parts in sealing engagement with the stator to define the helicalcavities. In transverse cross section the stator is usually providedwith either one lobe more or one lobe less than the rotor, in the lattercase the rotor having two or more lobes. Also the longitudinal geometriccenterline of the rotor generally translates about an eccentric axis toachieve the pumping action.

Accordingly, the prior art rotors are operatively connected to a rotarydrive by a universal connection to r accommodate the eccentrictranslation of the rotors longitudinal geometric centerline. Normallythe centerline translates through 360 at a rate n times the rotation ofthe rotor where n is the number of lobes on the rotor. In the case wherethe rotor has one lobe less than the stator the translation is in thedireciton opposite to rotor rotation, and where the rotor has one lobemore than the stator the translation is in the same direction as rotorrotation.

The shape of the stator in transverse section may be for example, ofpolar cycloidal form while the rotor may have a generally elliptical oroval form which one lobe more than the stator. A more specific exampleof a stator cavity transverse sectional form is a polar conchoid whichis defined as the locus of the end points of a straight line generatrixwhen its center point 0 is translated in a circle while the generatrixpivots about its center point 0 and continues to intersect an initialreference point on the orbit circle. In polar form the resultingconchoid has the general equation y=2e sin 0+L where y is the distancefrom the initial tangent reference point of the center 0 to an end ofthe generatrix, L is one-half the length of the generatrix,

e is the orbit radius and 0 is the angular position of the generatrixrelative to an initial reference position tangent to the circle throughwhich its center translates, the po nt of tangency being the same as theinitial reference point.

A specific example of this type of stator cavity in two dimensional formis disclosed in the U.S. patent to Planche, No. 1,340,625. This type ofdevice uses a stator having a cavity cross section in the form of apolar conchoid and an eccentric two lobe rotor which rotates andtranslates in an eccentric path within the stator with its end pointsalways in engagement with the stator walls. The width of the rotor isequal to the length of the generatrix of the polar conchoid and thecross section is symmetrical about the generatrix so that thegeometrical center translates about a center of eccentricity twiceduring each full revolution of the rotor. The rotor is connected to arotary drive by a spindle designed to accommodate the eccentric travelof the rotor.

Another related prior art device in three dimensional form is shown inthe U.S. patent to Moineau, No. 1,892,217. This device uses a threedimensional helical rotor and stator cooperating with one another toform sealed helical cavities or pockets which progress axially from oneend of the pump to the other as the rotor translates and turns. Therotor has one lobe less than the stator cavity and consequently thecenter of the rotor translates about a center of eccentricity in adirection opposite to the direction of rotor rotation. The final form ofthe three dimensional rotor of Moineau is similar to a corkscrew.Accordingly, the rotor shape and the cavity shape are diflicult tomachine or otherwise fabricate. Furthermore the Moineau rotor must beconnected to a rotary drive or rotary prime mover by means of auniversal connection in view of the nonplanar displacement of the rotorrelative to the drive shaft during the pumping operation.

Still another related prior art device is disclosed in the U.S. patentto Payne, No. 3,299,822. The Payne device utilizes a stator having aninternal surface with a cross section in the form of a cardioid, and arotor transverse section of generally elliptical form. In the Payneconstruction, because of a cusp which engages the rotor either at onelobe or along its side, there is provided, during most of the rotormovement, a three point contact, a cusp always being in contact with therotor. Due to the cusp or tooth a reduced sealing efficiency resultsfrom increased wear concentrated on the cusp. This wear destroysintimate contact between the cusp and the rotor and allows leakage.

Another disadvantage of prior art constructions is the difliculty incleaning the rotor and stator. In each instance the unit must bedisassembled and the rotor completely removed in order to gain access tothe cavity forming surfaces. The use of a split stator which rnay beseparated and removed from the rotor is not possible because of eitherthe presence of a cusp in some instances (thus requiring a diagonalsplit across a cusp which would quickly be worn to a gap) or thepresence of multiple lobes in the stator in other instances (thusrequiring a split or parting line extending diagonally across thereentrant portions of the lobes where the stator surface would make asharp angle with the plane of the split). Cleaning and disinfecting isparticularly important in the handling of foodstuffs where it must beaccomplished at intervals as short as every six hours of operation. Alsoit is desirable to be able to clean the pump without disturbing thepiping.

The pump construction of the present invention reduces the disadvantagesindicated above and affords other features and advantages not heretoforeobtainable.

3 SUMMARY OF THE INVENTION It is among the objects of the invention toreduce the wear while improving the sealing efiiciency between thestator and rotor of a progressing cavity, planetary rotor, helical pumpor motor of the type discussed.

Another object is to eliminate the need for a universal coupling betweenthe eccentric rotor and the rotary drive for the pump or motor.

A further object is to provide a dynamic fluid balance in the pump ormotor and thereby to eliminate unbalanced radial forces duringoperation.

Still another object is to provide a rotary pump or motor of the typediscussed wherein the stator may be of split construction to facilitatedisassembly without danger of excessive wear resulting at the partingline, so as to accommodate periodic cleaning such as is essential in thecase of the handling of foodstuffs.

A still further object is to provide a progressing helical cavity,planetary rotor type pump or motor with a stator cavity of conchoidaltransverse sectional form wherein cusps or teeth are eliminated and wearis distributed uniformly over the inner surface of the stator ratherthan being concentrated on cusps or teeth of the stator.

These and other objects are accomplished by a combined stator and rotorconstruction comprising a generally tubular stator having an interiorhelical surface with a transverse section in the form of a first closedplane figure defined by points spaced outwardly a distance r on normallines from the surface of a polar cycloid having n1 lobes and ageneratrix with a center that translates about a center of eccentricity.The interior helical surface is generated by translating the first planefigure along an axis extending perpendicular to the plane thereofthrough the center of eccentricity while rotating the closed planefigure about the axis. The ratio of the radius of the circumscribedcircle of the generatrix to the eccentricity is at least about n z-l.Within the stator cavity is a rotor having a helical surface with atransverse section in the form of a second plane figure of n symmetricallobes having rounded ends of radius r centered at the end points of thegeneratrix. The helical surface is generated by translating the secondplane figure along a rotor axis through its geometric center at n timesthe lead that the first plane figure twists about the stator axis. Therotor is turned in the stator by a rotary drive which simultaneouslyallows translation of the rotor axis about the center of eccentricity Pat n times the rate of rotation of the rotor.

In a preferred for-m the stator cross section is in the form of a polarconchoid and the rotor cross section is in the form of symmetricalquadrants divided by the straight line generatrix and its perpendicularbisector. The sides of the rotor cross section between the rounded endsare formed to match the interior surface of the stator when thecircumscribed center of the rotor cross section is located at an initialreference position on the circle through which the center point of thegeneratrix translates during its generating movement.

According to one aspect of the invention the rotor is a hollow body witha rather thin wall of substantially uniform thickness throughout itslength so that the centrifugal force of the rotor about the axis of therotary drive is about equal and opposite to that of the material in thecavities. Thus the fluid being passed through the pump acts as a counterbalancing medium which results in good dynamic balancing of the rotor.Also the connection between the rotary drive and the rotor is preferablyin the form of a coupling shaft connected at its ends by parallel hingepins to the rotary drive shaft on the one hand and the rotor on theother hand. This type of connection is sufiicient with rotors andstators embodying the present invention.

As another aspect of the invention, the stator is formed of two matchingsections split in an axial plane so that they may be easily removed fromthe rotor to facilitate cleaning. This eliminates any need fordisconnecting the associated plumbing or disconnecting the rotor fromthe rotary drive.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section of aprogressive cavity pump embodying the invention showing the rotor in aninitial reference position;

FIG. 2 is a transverse sectional view taken on the line 22 of FIG. 1;

FIG. 3 is a transverse sectional view taken on the line 33 of FIG. 1;

FIG. 4 is a transverse sectional view taken on the line 44 of FIG. 1;

FIG. 5 is a transverse sectional view taken on the line 5 5 of FIG. 1;

FIG. 6 is a side elevation of the pump of FIG. 1 with parts broken awayand shown in section, with the rotor turned from its reference positionof FIG. 1;

FIG. 7 is a transverse sectional view taken on the line 7-7 of FIG. 6,which corresponds to line 22 of FIG. 1;

FIG. 8 is a transverse sectional view taken on the line 8-8 of FIG. 6,which corresponds to line 3-3 of FIG. 1;

'FIG. 9 is a transverse sectional view taken on the line 99 of FIG. 6,which corresponds to line 44 of FIG. 1;

FIG. 10 is a transverse sectional view taken on the line 1010 of FIG. 6,which corresponds to line 55 of FIG. 1; and

FIG. 11 is a diagrammatic view showing the two dimensional geometricrelationships used in generating the stator cavity cross section and therotor cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly tothe drawings, and especially to FIGS. 1 and 6 there is shown aprogressing-cavity rotary pump embodying the invention and particularlyadapted for use in pumping foodstuffs such as milk, cottage cheese, piefilling and the like. The pump comprises a pump body 10, a generallytubular stator 11 preferably formed of rubber or other resilientmaterial and a helical rotor 12 received within the stator. The rotor 12is shown rotated 90 in FIG. 6 from the position shown in FIG. 1 and itwill be seen that during rotation the rotor center also translates in amanner to be described in more detail below. The stator 11 is receivedwithin a cylindrical metal sleeve 13 which is connected to the pump body10 at an exit opening of an intake chamber 14 and at the opposite end toa discharge reducer 17. The stator 11 and sleeve 13 are split in ahorizontal axial plane into two equal halves and the two halves of theshell 13 are connected along one edge by a hinge (not shown). The halvesare clamped together and to the pump body 10 and discharge reducer 17 byring clamps 15 at each end. With this arrangement the stator 11 andsleeve 13 may be quickly removed from the pump body 10 and rotor 12 forperiodic cleaning without disturbing the associated plumbing or therotary drive unit. Also mounted on the pump body is an inlet pipe 16which communicates with the intake chamber 14. The material to be pumpedis accordingly fed through the inlet pipe 16 in sufiicient quantity tosupply the pumping capacity of the pump.

Located at the opposite end of the stator 11 and rotor 12 is thedischarge reducer 17 through which the material being pumped is fed toits ultimate destination.

The rotor 12 is driven by a drive shaft 19 journaled in bearing units 20and 21 in the pump housing 10. The connection between the drive shaft 19and the rotor 12 is in the form of a coupling link 22 which is pivotallyconnected to the drive shaft by means of a hinge pin 23 extendingthrough the end of the drive shaft 19 and into the bifurcated end 24 ofthe coupling link 22. The link 22 is pivotally connected to the rotor 12at its other end by another hinge pin 25 having an axis parallel to theaxis of the pin 23 and extending through the end of a coupling link 22and into bearings 26 located in an end seal 27 secured to the inner endof the rotor 12. The opposite end of the hollow rotor is closed byanother end seal 28. The operation of the hinged coupling link 22 andthe advantages deriving therefrom are described in greater particularitybelow.

The stator 11 and rotor 12. define therebetween a series of sealedhelical cavities 31, 32, 33, and 34 which progress from the inlet end tothe discharge end of the pump during the rotation and translation of therotor. FIGS. 2 through 5 indicate the relationships between the rotortransverse cross section and the stator transverse cross section at fourequally spaced axial positions and the helical twist formed in both thestator and rotor surfaces will be apparent therefrom. It will be seenthat the cavities progress from a sealed end to a maximum cross sectionand then diminish to a sealing point. In the embodiment of the inventionillustrated herein the cavities extend twothirds the length of the rotorand stator or in other words the rotor and stator are one and one-halfcavity lengths long. It will be apparent in the embodiment shown thatportions of four different cavities will be present in the pump duringits operation.

FIGS. 7-10 show the cross sectional relationships at axial positionscorresponding to those of FIG. 1 after the rotor has been turned 90. Theprogression of the various cavities will be apparent from these views aswell as the fact that the rotor translates 180 about its center ofeccentricity during the illustrated 90 of rotor rotation about the rotorcenterline O-O. Also a new cavity 30 has started to form at the inletend of the rotor 12.

In order to assure the proper relationship between the rotor 12 and thestator 11 the stator is keyed to the inlet housing 10. This assures thatthe relationship between the stator centerline PP and the drive shaftaxis DD will be as shown for example in FIG. 7.

ROTOR AND STATOR GEOMETRY FIG. 11 will be used to illustrate the variousgeometrical relationships involved in the constmction of the rotor andstator surfaces. The line AB is the generatrix which determines thecross sectional form of both the rotor 12 and stator 11. It is used togenerate a conchoid (shown in dashed lines) by the translation of itscenter 0 about a center of eccentricity P and simultaneously rotatingthe generatrix AB about its center 0, the angular velocity of rotationbeing one-half of the velocity of translation and the direction oftranslation being the same as the direction of rotation. The positionshown will be referred to as the reference position of the generatrixAB. During the generating movement of the generatrix the locus of itsend points defines a polar conchoid shown in dashed lines, the polarequation of which is y=2e sin 0+L, wherein:

y=distance from the center of reference C to any point,

A, on the surface of the conchoid (the center of reference C is thepoint where line AB is perpendicular to a line connecting points 0 and Pand point 0 is superposed on point C); e=eccentricity or orbit radius;0=angle between line AB when in its reference position and when in itsinstantaneous position wherein point A is the point on the conchoiddescribed by the equation;

and L=one-half of line AB.

In FIG. 11 there is shown a radius, r, centered on point A and anotherradius of equal length centered on point B. Thus the conchoid describesthe locus of the centers of these two radii as they translate with thegeneratrix AB. The actual shape of the stator cross-section S thusformed is consequently larger than the conchoid by the radial distance,r, measured normal to the surface of the conchoid.

The rotor cross-section R may be best described with reference to thegeneratrix AB when in its reference position as shown in FIG. 11 wherethe geometric center 0 of the rotor is instantaneously superimposed onpoint C. It will be seen that the cross sectional form comprisessymmetrical quadrants defined by the generatrix AB as extended at eachend by radius (r), and the perpendicular bisector of AB. Each end of therotor cross section R is rounded by the radius (r) centered at points Aand B on the generatrix and the portions between the ends of these radiiare shaped so that the rotor fits exactly the inner surface of thestator when, and only when, the rotor is in its reference position shownin FIG. 11. During rotation of the two dimensional rotor, the rotorfollows the same path of motion as the generatrix AB in generating theconchoid within the stator cross section S.

This particular stator surface is simpler to generate in productionsince it allows room for a grinding wheel or rotary cutter of radius, r.

The sides of the new eccentric rotor now fit closely against the statorwall in either reference position AB or the reverse position BA. Thisreduces the cross sectional area of the cavities to zero at each end. Itis obvious, in a two-dimensional motion device, however, that thiscondition of zero terminal volume is not essential to performance as apump or expander. In a helical device, however, the side wall of therotor cross section becomes a sealing line and a close fit is essentialto leakage control.

The three-dimensional geometric form of the twisted rotor 12 is createdas follows:

We take the eccentric rotor section R and twist it about its center, 0,within the conchoidal stator section S axially extended. At the sametime we translate the geometric center 0 about the eccentric center P,so that normal planes passed through the rotor at axial intervals of onepitch length will show the rotor within the stator in exactly the samepositions relative to the reference position shown in FIG. 11. Thisrepresents of rotation of the rotor section R and 360 of translation ofpoint 0 around the eccentric circle. The twist about center 0 is exactlyat onehalf the rate of translation of 0 about center P or in otherwords, the lead of the twist about 0 is twice as long as the lead of thehelix 0 about P.

In the form, however, the device is useless in a practical sense sinceit is now locked against motion and the helical rotor cannot be rotatedwithin the stator.

Next we take the eccentric path of motion of center 0 about center P andimpart another helical twist to the entire unit, that is, the axiallyextended stator section as well as the newly formed helical rotor. Thisnew twist is in a direction opposite to the two initial twists alreadygiven the helical rotor and it occurs about centerline, PP, which is astraight line while centerline OO has a twist in it centered about PP asdescribed above. If we consider the two twists already in the helicalrotor to be in a counterclockwise direction, the new twist is in aclockwise direction about centerline PP and it has a lead length equalbut opposite in direction to the helical shape of centerline 0-0. Theresult of this rotational twist is that the stator takes on a helicalshape since the stator conchoid has unequal radial dimensions withrespect to line PP. Also, we find that the twisted line OO becomesstraight and that the twisted plane AABB is untwisted from itscounterclockwise direction and re-twisted in a clockwise direction. Thelead of the twist of plane AA BB about the straight centerline O-O istwice as long in a clockwise direction as the lead of the twist in thestator about straight centerline PP also in a clockwise direction.

Since in any cross section taken along the axial length, theintersection with lines OO and PP will occur in the same angularposition, it is possible now to rotate the helical rotor aboutcenterline O-O and simultaneously to translate centerline O'--O aboutaxis P--P in the same manner as with the two-dimensional device. Duringrotation of the helical rotor the generatrix AB at any section followsthe same path as that in the case of the twodimensional device describedabove.

The result of this motion is to cause an axial translation of eachcavity 31, 32, 33, and 34 not unlike the passage of a wave along itspath of translation. This w-avelike motion is complex since it occursalong a helical path.

Each cavity is sealed by contact between the twisted rotor 12 and thestator inner surface. This contact would occur along lines AA and -BB ifsharp edges were used, however, with the provision of a surface radiuscentered on lines AA and BB according to this invention and as outlinedin the description of the two-dimensional device, this contact lineoccurs between the twisted rotor convex radius and the stator concaveradius and furthermore it traverses the entire surface of the radius ofthe rotor so that rotor wear is uniformly distributed on the rotorradius. At the terminal ends, the cavities are sealed 'by virtue of theaccurate fit between the rotor and stator surfaces. These terminal seallines of course, travel in wavelike translation as the prescribedrelative motion occurs and thus follow the path of the cavities.

This wave-like cavity motion is useful as a pump or as a hydraulic motorsince, at the inlet end of such a device the cavity grows to maximumvolume as it progresses and then remains at maximum volume while ittranslates toward the discharge end. The cavity begins to decrease involume when the leading end passes the discharge edge of the housing.When the trailing edge reaches the discharge end the cavity reaches zerovolume and disappears.

By sealing the ends of the cavities in this manner there is created anew family of gear mechanisms based upon high eccentricity ratios wherethe eccentricity ratio, R is described as the ratio of one-half thelength of line AB to the eccentricity, e, i.e.

Re= e It has been found that when this ratio is under 4:1 the innersurface of the stator closest to the orbit center P begins to develop aconvex characteristic. A convex surface here would tend to cause therotor to lock itself to the outer member at the reference positionwhenever the inner member is made to fit the outer member in thereference position.

Accordingly, the device of this invention will for the most part berestricted to mechanisms wherein the ratio R is greater than 3:1 andpreferably greater than 4: 1.

It is evident that the length of the line L(1cos 4)) must be greaterthan line e( lcos 2) to avoid convexity in the outer member at thispoint, i.e.

where is the angle of rotation of the generatrix relative to a linewhich passes through both the orbit center, P, and the initial referenceposition of O.

The largest value of this ratio occurs at =O or when l-l-cos =2 thus Itshould be evident that this same result can be achieved with rotorswhich have more than 2 lobes. Where the stator has more than one lobethe generatrix becomes a plane figure such as an equilateral triangle(two stator lobes) or other equilateral polygon having a radius of itscircumscribed circle L. In these cases the eccentricity ratio will begreater than in the case of a two-lobed rotor. For example L/e=4, 9, 16,etc., for one lobe, two lobes or three lobes respectively.

The rotor 12 can be manufactured from steel or aluminum tubing of properwall thickness by one of the following expansion processes:

(a) hydraulic tube expansion (b) electro-hydraulic, high-velocity tubeexpansion (c) explosive forming (d) electro magnetic forming Previousrotor shapes have not lent themselves to these methods either because oftheir helical centerlines or because of their restricted cross sectionalareas.

HINGED COUPLING The device described herein lends itself to the use ofthe simplified type of drive coupling 22 which has flexibility in onlyone plane as opposed to the full directional flexibility requiredheretofore. This type of joint will be referred to as a hinge joint.

Referring to FIG. 11 it will be noted that with respect to rotormovement as described above, line AB of the rotor always passes throughthe reference position C of point 0 no matter what position the rotor isrotated to.

If a simple hinge pin is connected to the drive shaft 19 centered on thereference position C and a second similar hinge pin is connected on therotor 12 at point 0 when point 0 is at the reference position C, and ifthe pins of these two joints are aligned parallel to each other andperpendicular to an axial plane through line AB and further if these twojoints are connected to each other by a rigid coupling shaft, then thedouble hinge joint will always have its plane of flexibility parallel toand passing through the line AB no matter which angular position theline AB is rotated into. This simple coupling will then be capable offollowing and of transmittingtorque to the rotor 12.

The use of this simple hinge joint effects substantial savings in thecost of the helical device drive system. A second and equally importantadvantage is that the journal type bearings 26 may be used with thehinge pin joint. This type of bearing has much greater load carryingcapacity than does the modified universal type of flexible coupling.where most of the load bearing surface of the journal is cut away toprovide the full flexibility needed in this type of joint. Also ifdesired the rotor can be detachably connected to its hinge pin to permitquick removal for cleaning, since all axial forces are tending to pushthe rotor against the rotor drive.

DENSITY BALANCED ROTOR The required orbiting of the rotor 12 has adisadvantageous result in that the centrifugal forces arising from theorbit motion set up vibrations within the pump, or motor frame causingnoise and instability and limiting the speed of the device.

The enlarged cross sectional area of the rotor 12 which results fromadding the radii at points A and B (FIG. 11) and from expanding thesides of the rotor to fit the stator 11, allows the rotor to be designedwith a hollow interior and a relatively thin wall section.

Since this wall is located at a relatively greater distance from therotor center than the walls of other similar helical gear mechanisms,the torsional stress for a given torque will be substantially less.Furthermore the straight rotor centerline OO further enhances the torquecapacity of the rotor as compared to devices having a rotor which therotor sections are arranged about a helical centerline.

This greatly enhanced torque capacity allows the wall thickness to bereduced to the point where the rotor density is equal to that of thefluid being pumped or being used to power the motor (assuming that therotor is empty and sealed at each end). Since the fluid circulateswithin the outer member at the same average angular velocity as therotor orbit velocity, the rotor 12 tends to float in the fluid toprovide a zero net unbalance force with the fluid itself acting as thecounter balance m edium.

It will be apparent that pumps or motors of greater axial length havingmore cavities in series may be used if desired to increase the pressurehandling capability.

9 SPLIT STATOR CONSTRUCTION As indicated above, the stator 11 and shell13 are of split construction with the split 35 lying in an axial plane.This type of construction is possible and feasible only because asindicated in FIGS. 2 to 5 the plane of the split 35 intersects theinterior helical surface of the stator 11 at approximately right anglesthroughout the length of the stator. Thus there are no sharp acuteangles in the abutting rubber edges along the split line which might besubject to excessive wear.

The elimination of sharp angles at the intersection of the interiorsurface of the stator and axial planes through the stator is achieved byenlarging the polar conchoid of FIG. 11 (dashed lines) by a distance rand by using a relatively high eccentricity ratio R i.e. at least 3:1and preferably 4:1 or greater so as to eliminate cusps or teeth. As Willbe seen from FIG. 11 this substantially rounds out the stator crosssection as compared with the conchoid from which it is derived.

The two halves of the shell 13 may be hinged together along one splitline if desired to assure proper axial alignment with one another wheninstalled. To remove the stator and shell one need merely remove thering clamps 15 which secure the shell 13 to the pump body 10 anddischarge reducer 17, and then separate the halves thus removing themfrom the rotor.

While the invention has been shown and described with reference to aspecific embodiment thereof, this is intended for the purpose ofillustration rather than limitation and variations and modificationswill become apparent to those skilled in the art within the intendedspirit and scope of the invention as herein specifically illustrated anddescribed. Therefore the patent is not to be limited in scope and effectto the preferred form shown herein nor in any other way that isinconsistent with the extent to which the progress in the art has beenadvanced by the invention.

What is claimed is:

1. A progressing-cavity, positive displacement helical pump comprising agenerally tubular stator having an interior helical surface. generatedby translating a first closed plane figure, defined by points spacedoutwardly a distance :r on normal lines from a closed polar cycloidalfigure having n1 lobes and a generatrix center that translates about acenter of eccentricity, along a perpendicular axis through said centerof eccentricity While rotating said first plane figure about said axis,the ratio of the radius of the circumscribed circle of the generatrix ofsaid polar cycloidal figure, to the eccentricity being at least about n:l; a rotor received in said stator and having a helical surfacegenerated by translating a second closed plane figure of n symmetricallobes having rounded ends of radius r centered at the end points of saidgeneratrix, along a rotor axis perpendicular to said second plane figureat its geometric center, at n times the lead that said first planefigure rotates around said first named axis, and

rotary drive means for turning said rotor in said stator while saidrotor axis translates in the same direction about said center ofeccentricity at n times the rate of rotation of said rotor.

2. A progressing-cavity, positive displacement helical pump comprising agenerally tubular stator having an interior helical surface generated bytranslating a first closed plane figure defined by points spacedoutwardly a distance. r on normal lines from a polar conchoid having astraight line generatrix with a center that translates about a center ofeccentricity, along a perpendicular axis through said center ofeccentricity, while rotating said first plane figure about said axis,the ratio of the radial length of said generatrix to the eccentricitybeing at least 3:1; a rotor received in said stator and having a helicalsurface generated by translating a second closed plane figure, ofsymmetrical quadrants divided by said generatrix and its perpendicularbisector, and having rounded ends of radius r centered at the ends ofsaid generatrix, along a rotor axis perpendicular to said second planefigure at its geometric center at twice the lead that said first plane.figure rotates around said first named axis, and rotary drive means forturning said rotor in said stator While said rotor axis translates aboutsaid center of eccentricity at twice the rate of rotation of said rotor.

3. Apparatus as defined in claim 2 wherein said ratio is at least 4:1.

4. Apparatus as defined in claim 1 wherein said rotor has a uniform Wallthickness throughout its length.

5. Apparatus as defined in claim 4 wherein the center of gravity of therotor and material being pumped,in a radial plane, is at the axis of therotary drive.

6. Apparatus as defined in claim 2 wherein said rotor is connected tosaid rotary drive means by a coupling link pivotally connected by afirst hinge joint at one end to said rotary drive and pivotallyconnected by a second hinge joint at the other end to said rotor, saidhinge joints having their respective axes parallel to one another.

7. Apparatus as defined in claim 1 wherein said stator is split in anaxial plane to form two equal connectible matching halves whereby saidstator may be removed from said rotor.

References Cited UNITED STATES PATENTS Re. 21,374 2/19-40 Moineau.

2,463,341 3/ 1949 Wade. 2,464,011 3/ 1949 Wade. 2,874,534 2/ 1959Canazzi. 3,165,065 1/ 1965 Stickel. 3,203,350 8/ 1965 Chang. 3,299,8221/ 1967 Payne.

WILLIAM L. FREEH, Primary Examiner W. J. GOODLIN, Assistant Examiner

